Micro-mechanical adjustment system for piezoelectric transducers

ABSTRACT

A system for detecting blood velocity within a blood vessel includes a transducer array including a plurality of transducers. Each of the transducers includes a carrier substrate, at least one spacer extending upwardly from the substrate, a transducer element attached to the spacer such that the piezoelectric transducer is spaced apart from the substrate, and setting electrodes positioned on the upper surface of the substrate under the piezoelectric transducer. The system also includes a tilt control system that is configured to apply a bias voltage to the setting electrodes which causes the transducer element to pivot about a pivot axis between a first tilted position and a second tilted position.

TECHNICAL FIELD

The disclosure is related generally to systems and methods for measuringblood velocity, and, in particular, to systems and methods for measuringblood velocity using phased arrays.

BACKGROUND

Currently, there is no non-invasive small wearable sensor which is ableto detect the blood pressure of a human test subject. Non-invasive bloodestimation has a lot of medical and personal benefits. In a lot ofsituations detecting the stress level of people could prevent heartattacks or avoid burn out diseases if the blood pressure is monitoredover a longer period of time. Therefore there is the need of a sensorwhich is able to estimate blood pressure which enables to monitor theblood pressure over longer periods of time.

One of the main challenges of the measurement principle described insection will be to find the exact position of the artery in relation tothe transducer array with a very high angle resolution. For the bloodvelocity measurement, it is necessary to know this angle precisely sothe artery can be scanned correctly to achieve the best signal quality(SNR) and to minimize power in a wearable device. Therefore a newconcept which is able to detect the position of the artery with highspatial and angular resolution will be proposed in this patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an ultrasonic piezoelectric transducer 10 according toone embodiment of the disclosure.

FIG. 2 depicts an embodiment of a system 30 for detecting blood velocityand measuring blood pressure using the piezoelectric transducer 10 ofFIG. 1.

FIG. 3 depicts an alternative embodiment of a piezoelectric transducerfor use with the system of FIG. 2.

FIG. 4 depicts another alternative embodiment of a piezoelectrictransducer for use with the system of FIG. 2.

FIG. 5 depicts a 1×N array of transducer elements for a phasedtransducer array.

FIG. 6 depicts an N×1 array of transducer elements for a phasedtransducer array.

FIG. 7 depicts an M×N array of transducer elements for a phasedtransducer array.

FIG. 8 is a schematic depiction of a phased transducer array with beamsteering along an X axis of the array.

FIG. 9 is a schematic depiction of a phased transducer array with beamsteering along an Y axis of the array.

FIG. 10 is a schematic depiction of a phased transducer array depictinga measurement angle for the transducer.

FIG. 11 depicts an embodiment of a transducer element for a phasedtransducer array.

FIG. 12 schematically depicts a phased array transducer misaligned withrespect to a blood vessel.

FIG. 13 schematically depicts a side view of the phased array transducerof FIG. 12.

FIG. 14 is a top view of a piezoelectric transducer havingmicro-mechanical adjustment means.

FIG. 15 is an elevational view of a first side of the transducer of FIG.14.

FIG. 16 is an elevational view of a second side of the transducer ofFIG. 14.

FIG. 17 shows the piezoelectric transducer of FIG. 14 in a first tiltedposition.

FIG. 18 shows the piezoelectric transducer of FIG. 14 in a second tiltedposition.

FIG. 19 is a block diagram of a combined multi-input multi-output (MIMO)array and phased array blood velocity detection system.

FIG. 20 is a schematic diagram of a bistatic version of the combinedmulti-input multi-output (MIMO) array and phased array blood velocitydetection system of FIG. 19.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and described in the following written specification. It isunderstood that no limitation to the scope of the disclosure is therebyintended. It is further understood that the present disclosure includesany alterations and modifications to the illustrated embodiments andincludes further applications of the principles of the disclosure aswould normally occur to one of ordinary skill in the art to which thisdisclosure pertains.

An ultrasonic piezoelectric transducer 10 according to one embodiment ofthe disclosure is depicted in FIG. 1. The ultrasonic piezoelectrictransducer 10 includes a piezoelectric substrate 12, an upper electrode14 and a lower electrode 16. The piezoelectric substrate 12 is formed ofany suitable piezoelectric material including, for example, leadzirconate titanate or aluminium nitride. If the fabrication of thesensor device involves CMOS processes, aluminium nitride mayadvantageously be used because aluminium nitride is compatible with CMOSprocesses.

The upper and lower electrodes 14, 16 are formed of a conductive metal,such as aluminum, aluminum alloy, platinum, tantalum, or any othersuitable conductive metal. As depicted schematically in FIG. 1, theupper and lower electrodes 14, 16 are configured to be electricallyconnected to a signal control system 18 which includes signal generatingand/or receiving components.

The piezoelectric transducer 10 is supported on a carrier substrate 20.The carrier substrate 20 serves as a carrier for the piezoelectrictransducer 10 and also as a coupling member for coupling the signalsgenerated by the piezoelectric transducer 10 to underlying skin andtissue. The substrate 20 includes a lower surface 22 and an uppersurface 24. The lower surface 22 of the substrate 20 is configured to beplaced against a planar surface 26, such as a planar area of skin on apatient's body. The upper surface 24 is on an opposite side of thesubstrate from the lower surface 22 and is a generally planar surface towhich the piezoelectric transducer 10 is attached.

The upper surface 24 is configured to orient the piezoelectrictransducer 10 at a fixed non-zero angle with respect to the planarsurface 26. To this end, the substrate 20 is fabricated in a manner thatresults in the upper surface 24 of the substrate 20 being tilted at apredetermined angle α with respect to the lower surface 22 of thesubstrate 20. The predetermined angle α corresponds to the desired angleof incidence at which the ultrasonic signals, or ultrasonic waves,emitted by the transducer.

The angle of incidence is the angle between a plane defined by the lowersurface 22 of the substrate 20 or by the planar surface 26 and a line Lthat is perpendicular to the planar surface of the transducer 10 thatintersects the plane. The upper surface 24 of the substrate isconfigured to orient the piezoelectric transducer at a predeterminedangle of incidence α that is greater than 0° and less than 90°. Thepredetermined angle of incidence α enables a single piezoelectrictransducer 10 to be used to determine the blood velocity based on theDoppler Effect (explained in more detail below).

In addition to supporting the transducer 10 at a fixed incident angle αwith respect to the planar surface 26, the substrate 20 is alsoconfigured to serve as a coupling member for coupling the ultrasonicsignals between the piezoelectric transducer 10 and the underlying skinupon which the substrate is placed. Preferably, the substrate 20 isformed of steatite ceramic because steatite ceramic makes a drytransition to skin. Alternatively, any suitable substrate material maybe used.

FIG. 2 depicts an embodiment of a system 30 for detecting blood velocityand measuring blood pressure using the piezoelectric transducer 10 ofFIG. 1. The system 30 is a bistatic system including a single ultrasonicpiezoelectric transmitter 10 a and a single ultrasonic piezoelectricreceiver 10 b. The transmitter 10 a and receiver 10 b each have the sameangle of incidence α and are arranged in mirror symmetry with respect toeach other. In one embodiment, the transmitter and receiver 10 a, 10 bare incorporated into a housing 28 which retains the transmitter andreceiver 10 a, 10 b at fixed positions in relation to each other. Thehousing 28 may be configured as a handheld device housing and/or may beincorporated into a wearable article which can be worn on a part of auser's body, such as the arm, leg or chest of a user.

The system 30 includes a signal generator 32 which is electricallyconnected to the piezoelectric transmitter 10 a. The signal generator 32is configured to actuate the piezoelectric transmitter 10 a to produce adesired ultrasonic signal 38. To take advantage of the Doppler Effect todetermine the blood velocity, the signal generator 32 is configured toactuate the piezoelectric transmitter 10 a to transmit an ultrasonicsignal in a pulsed or continuous wave fashion with a predeterminedfrequency. In one embodiment, the predetermined frequency is in a rangefrom 2 MHz to 10 MHz. In one particular embodiment, the predeterminedfrequency is approximately 4 MHz.

The ultrasonic signal is directed toward the blood vessel 36 at an anglethat depends on the angle of incidence α of the transducer 10 a and isreflected by the blood vessel 36. The piezoelectric receiver 10 breceives the reflected ultrasonic signal 40 and converts the signal to acorresponding electrical signal. A signal processor 34 is electricallyconnected to the piezoelectric receiver 10 b and is configured toprocess the electrical signals to determine blood velocity in the bloodvessel.

In one embodiment, the signal processor 34 is configured to evaluate theelectrical signals from the piezoelectric receiver 10 b to determine theradial velocity of the blood based on the Doppler Effect. For example,the received signal 40 has a Doppler shift due to the movement of theblood cells. The signal processor is configured to determine the Dopplershift of the received signal and to calculate a radial velocity of theblood as a function of the Doppler shift. The signal processor may beconfigured to determine the radial velocity of the blood from theDoppler shift in any suitable manner known in the art.

The signal processor may also be configured to determine a value for theblood pressure within the blood vessel. As is known in the art, there isa direct relationship between the blood velocity in a blood vessel andblood pressure. Therefore, once the blood velocity has been determined,an estimated value of the blood pressure can be determined as well. Thesignal processor may be configured to determine the blood pressure valuefrom the blood velocity in any suitable manner.

For actuating the piezoelectric transducers 10 a, 10 b and processingreceived signals, the signal generating and processing devices 32, 34may include a processor (not shown), such as a central processing unit,an application specific integrated circuit (ASIC), a field programmablegate array (FPGA) device, or a micro-controller. The processor may beconfigured to execute programmed instructions that are stored in amemory (not shown).

Referring now to FIG. 3, an alternative embodiment of a piezoelectrictransducer 10′ is depicted which may be used with the blood velocitydetection and blood pressure measurement system 30 of FIG. 2. Thepiezoelectric transducer 10′ of FIG. 3 is a distributed piezoelectrictransducer. The distributed piezoelectric transducer 10′ is formed bydividing the piezoelectric transducer 10 of FIG. 1 along one dimensioninto a plurality of separate, smaller transducers 42. The plurality oftransducers 42 are connected together in a row and operated as a singlepiezoelectric transducer.

As depicted in FIG. 3, each of the transducer elements 42 is provided ona separate substrate which is preferably formed of steatite ceramic. Theupper surface 24 of each of the substrates 20 is a planar surface thatis arranged to provide an angle of incidence α that is greater than 0°and less than 90° in the same manner as the upper surface 22 of thesubstrate 20 in FIG. 1. Because the transducer elements 42 are smallerthan the transducer 10 of FIG. 1, the distributed transducer 10′ canhave the same effective width as the single element transducer 10 ofFIG. 1 while enabling a significant reduction in height h as compared tothe transducer 10 of FIG. 1. Higher angles of incidence therefore can beachieved with a distributed transducer without resulting in asignificant increase in the overall height of the transducer.

In the embodiment of FIG. 3, the plurality of transducers 42 form onerow of transducers, i.e. a 1×N array where N is the number of transducerelements (five in this case). Each of the transducers 42 is oriented inthe same direction with the same angle of incidence α. In alternativeembodiments, the transducers 42 can be provided with different angles ofincidence and can be oriented in different directions. FIG. 4 depicts anembodiment of a distributed transducer 10″ having transducer elements 42a, 42 b which are oriented in two different directions. In thisembodiment, each of the transducer elements 42 a, 42 b is configured tohave the same angle of incidence. The transducer 10″ of FIG. 4 could beconfigured as a bistatic system with the elements 42 a being groupedtogether to serve as a transmitter and elements 42 b being groupedtogether to form a receiver. In another example (not shown), thetransducer elements could be arranged to form pyramid structures inwhich four transducer elements are oriented in four different directionswith the same angle of incidence.

To avoid coupling between the different transducer elements 42, anisolation layer 44 may be added onto the edges of the substrate 20 todamp or reflect ultrasound signals from adjacent transducer elements 42.An example of an isolation layer 44 on a transducer is depicted inFIG. 1. Any suitable type of material may be used for the isolationlayer 44.

Referring now to FIGS. 5-10, another embodiment of a system 30 fordetecting blood velocity and measuring blood pressure is depicted. Inthe embodiment of FIGS. 5-10, the system 45 includes a phased transducerarray 46 for generating and receiving the ultrasonic signals which areused to detect artery location and measure blood velocity.

A phased transducer array 46 includes an array of piezoelectrictransducer elements 48 arranged on a substrate. The transducer array 46may comprise any number of elements along the X axis and Y axis of thearray. For example, the array may comprise a 1×N array of transducers asdepicted in FIG. 5 which has one element along the X axis and N (in thiscase five) elements along the Y axis, or the array may comprise an N×1array as depicted in FIG. 6 where N elements (in this case five) areprovided along the X axis and one element is provided along the Y axis.A transducer array having a dimension with a single element is alsoreferred to as a transducer row. The array 46 may also comprise an M×Narray of transducers where M is the number of elements in along the Xaxis of the array and N is the number of elements along the Y axis ofthe array and M and N are greater than one. In FIG. 7, the array is a5×5 array of transducer elements 48.

The parameter p is the pitch distance between the center of onetransducer element 48 and the center of an adjacent transducer element48. The distance p is advantageously smaller than half the wavelength ofthe signal emitted by the array. The wavelength of signal is given bythe following equation:λ=v/fwhere λ is the wavelength of the signal, v is the ultrasonic velocity(for PZT: v≈3200 m/s, for human tissue: v≈1560 m/s), and f is thefrequency of the signal. For a transducer array to be operated around afrequency of 4 MHz, the wavelength is approximately 0.80 mm. Therefore,the pitch p in this case should be approximately 400 μm.

In one embodiment, each transducer element 48 has substantially the samesize and shape with the shape of each element being rectangular orsquare. The transducer elements 48 in the array 46 are fed an electricalsignal from a phase control system 62 simultaneously which causes eachtransducer element 48 to emit an ultrasonic signal or wave.

As is known in the art, the phase of the signals being fed to thedifferent elements may be controlled so that the effective radiationpattern of the array is reinforced in a desired direction and suppressedin undesired directions so that the main lobe, or beam, of the radiationpattern is pointed in the desired direction. By adjusting the phases ofthe signals fed to the elements, the direction of the beam may bechanged in a process called beam steering. Accordingly, an adjustablephase shifter (not shown) is associated with each element 48 in thearray 46 which enables the phase of the electrical signal being fed tothe transducer element 48 to be shifted.

As depicted in FIG. 8, a phased array 46 having more than one element 48along the X axis (i.e., the axis parallel to the longitudinal dimensionof the blood vessel and the direction of blood flow) enables beamsteering along the X axis. This enables the angle component θ of thebeam to be adjusted. The angle component θ controls the angle ofincidence of the beam with respect to the blood vessel 36. Similarly, aphased array 46 having more than one element 48 along the Y axis (i.e.,the axis perpendicular to the blood vessel and the direction of bloodflow) enables beam steering along the Y axis as depicted in FIG. 9. Thisenables the angle component ϕ to be adjusted. With the angle component θset to the angle of incidence for the transducer 46, scanning the beamalong the Y axis can be used to find the measurement angle ϕ_(v) wherethe blood vessel 36 is located as depicted in FIG. 10.

A phased array control system 62 is used to control the phase shiftingof the transducer elements 48 to produce a beam in the desireddirection. The control system 62 includes a processor (not shown), suchas a central processing unit, an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) device, or amicro-controller. The processor may be configured to execute programmedinstructions that are stored in the memory (not shown). The instructionsinclude instructions for phase shifting and/or for implementing one ormore beam steering algorithms.

An embodiment of a transducer element 48 for use in a phased transducerarray is depicted in FIG. 11. Similar to the transducer of FIG. 1, thetransducer element 48 includes a piezoelectric substrate 50, an upperelectrode 52 and a lower electrode 54. The piezoelectric substrate 50 isformed of any suitable piezoelectric material including, for example,lead zirconate titanate or aluminium nitride. The upper and lowerelectrodes 52, 54 are formed of a conductive metal, such as aluminum,aluminum alloy, platinum, tantalum, or any other suitable conductivemetal.

The transducer element 48 is supported on a carrier substrate 56. Thecarrier substrate 56 serves as a carrier for the transducer element 48and also as a coupling member for coupling the ultrasonic signals tounderlying skin and tissue. The substrate 56 includes an lower surface58 and an upper surface 60. The lower surface 58 is configured to beplaced against a planar surface 26, such as a planar area of skin on apatient's body. The upper surface 60 is on an opposite side of thesubstrate from the lower surface 58 and is a generally planar surface towhich the transducer element 48 is attached.

To avoid coupling between the different transducer elements 48 of thearray 46, an isolation layer 64 may be added onto the edges of thesubstrate 56 to damp or reflect ultrasound signals from adjacenttransducer elements 48. Any suitable type of material may be used forthe isolation layer 64.

The upper surface 60 is configured to orient the transducer element 48with respect to the surface 26 of the skin. For a two-dimensional array,such as depicted in FIG. 7, beam steering can be used to adjust theangle component θ so a fixed angle of incidence is not required for thetransducer. Therefore, the transducer can be arranged parallel to thesurface 26 which results in the transducer lying substantially flat onthe substrate.

In one embodiment of the system 45, the angle of incidence of thetransducer elements 48 is set to a fixed value which enables the radialcomponent of the blood velocity to be determined. This can beaccomplished by actuating the transducer elements 48 with static, phaseshifted electrical signals that cause the beam to be emitted at thedesired angle of incidence. The transducer elements arrayed along the Yaxis enable beam steering to be used to locate the measurement angleϕ_(v) in which the blood vessel 36 is located (FIG. 10). In thisembodiment, the system may be configured as a bistatic system, such asdepicted in FIG. 2, with one phased transducer array configured as atransmitter and one phased transducer array configured as a receiver.

In an alternative embodiment, the phased array 46 of may be provided asa transducer row with a single element width along the X axis to reducethe number of elements required for the array. In this embodiment, angleof incidence of each element 48 is fixed to enable the radial componentof the blood velocity to be determined. This can be accomplished in thesame manner as in the embodiment of FIG. 1, e.g., by orienting the uppersurface of the substrate at the desired angle of incidence.

The use of phased array transducers enables correction of misalignmentof the transducer array 46 with respect to the blood vessel 36. Forexample, FIG. 12 depicts a phased transducer array 46 which ismisaligned with respect to the blood vessel 36 by an angle β. Tocompensate for the misalignment during the determination of the radialvelocity of the blood, the angle β must be determined. This can be doneusing a triangulation method. More specifically, the angle β may bedetermined using the angle θ which corresponds to the incident angle andthe angle ϕ which is related to the measurement angle where the bloodvessel 36 is located.

Referring to FIGS. 12 and 13, to determine the misalignment angle β, thephased transducer array 46 is actuated at a first angle θ₁, and themeasurement angle ϕ₁ at which the blood vessel 36 is located isidentified. The beam is then steered to a second angle θ₂, and themeasurement angle ϕ₂ at which the blood vessel 36 is located isidentified. The distances to the blood vessel 36 at the first and thesecond measurement angles ϕ₁, ϕ₂ can then be determined which enablesthe blood flow direction to be identified. Because the central axis ofthe array 46 is known, the misalignment angle β can be determined sothat the misalignment angle β can be compensated for in calculating theradial component of the blood velocity.

As an alternative to beam steering with phase shifting, micro-mechanicalmechanisms may be used to adjust the incident angle and/or themeasurement angle of the transducer in compensating for misalignment ofthe transducer with respect to the blood vessel. An embodiment of apiezoelectric transducer having a micro-mechanical adjustment mechanismis depicted in FIGS. 14-16. As depicted, the piezoelectric transducer 70includes a piezoelectric substrate 72, an upper electrode 74 and a lowerelectrode 76. The upper and lower electrodes 74, 76 are formed of aconductive material, such as poly-silicon. The piezoelectric substrate72 is formed of a suitable piezoelectric material, such as leadzirconate titanate or aluminium nitride.

The transducer 70 comprises an element of a phased array 46, such asdepicted in FIGS. 5-10. The transducer 70 is supported on a carriersubstrate 78 which may be formed of silicon although any suitablematerial may be used. The transducer 70 is suspended over the substrate78 by a micro-mechanical adjustment system 80 that enables thetransducer 70 to pivot about a pivot axis P between a first tiltedposition (FIG. 17) and a second tilted position (FIG. 18). Themicro-mechanical adjustment system 80 includes one or more spacers 82,84 which are configured to space the transducer 70 apart from thesubstrate 72 to form a gap G between the substrate 78 and the lowerelectrode 76.

In the embodiment of FIGS. 14-16, the adjustment system 80 includes afirst spacer 82 and a second spacer 84. As depicted in FIG. 14, thefirst spacer 82 is positioned proximate a first corner of the substrate78 outside of the region over which the transducer 70 is located, andthe second spacer 84 is positioned proximate a second corner which isopposite from the first corner and outside the region of the substrateover which the transducer 70 is located.

The first and second spacers 82, 84 are connected to the transducer 70by first and second support arms 86, 88, respectively. The first supportarm 86 extends from an upper portion of the first spacer 82 and isconnected to the upper electrode 74 of the transducer 70, and the secondsupport arm 88 extends from the upper portion of the second spacer 84and is connected to the lower electrode 76 of the transducer 70. Thefirst and second spacers 82, 84 and the first and second support arms86, 88 are formed of an electrically conductive material, such aspoly-silicon, and are used to electrically connect the upper and lowerelectrodes 74, 76, respectively, to control and read-out circuitry.

The tilting of the transducer 70 to the first and second tiltedpositions is controlled by setting electrodes 90, 92 which are providedon or in the upper portion of the substrate 78. The setting electrodes90, 92 are formed of a conductive material, such as poly-silicon. In theembodiment of FIG. 15, the setting electrodes 90, 92 are formed in aninsulator layer 94 formed on the upper surface 96 of the substrate 78.The insulator layer 94 is formed of an insulating material, such assilicon dioxide.

The setting electrodes comprise a first setting electrode 90 and asecond setting electrode 92. The first setting electrode 90 is locatedon the substrate 78 under a first side portion 98 of the transducer 70which is positioned on a first side of the pivot axis P. The secondsetting electrode 92 is located on the substrate 78 under a second sideportion 100 of the transducer 70 which is positioned on a second side ofthe pivot axis P. The first and second setting electrodes 90, 92 areisolated from each other by the insulator layer 94.

As depicted schematically in FIG. 15, a tilt control system 102 iselectrically connected to the first and second setting electrodes 90,92. The tilt control system 102 is configured to selectively apply abias voltage to the setting electrodes 90, 92 for causing the transducer70 to pivot to the first and the second tilted positions.

When the tilt control system 102 applies the bias voltage to the firstsetting electrode 92, a potential difference is created between thefirst setting electrode 90 and the lower electrode 76 on the first sideportion 98 of the transducer which causes the first side portion 98 ofthe transducer 70 to be drawn downwardly toward the substrate 78. As thefirst side portion 98 moves downwardly, the transducer 70 pivots towardthe first tilted position (FIG. 17) resulting in the second side portion100 of the transducer 70 moving upwardly, farther away from thesubstrate 78.

When the tilt control system 102 applies the bias voltage to the secondsetting electrode 92, a potential difference is created between thesecond setting electrode 92 and the lower electrode 76 on the secondside portion 100 of the transducer 70 which causes the second sideportion 100 to be drawn downwardly toward the substrate 78. As thesecond side portion 100 moves downwardly, the transducer 70 pivotstoward the second tilted position (FIG. 18) resulting in the first sideportion 98 of the transducer moving upwardly, farther away from thesubstrate 78.

When the bias voltage is applied to the first setting electrode 90, thetransducer 70 pivots until the first side portion 98 contacts thesubstrate 78 or the insulator layer 94 on the substrate 78. Theorientation of the transducer 70 when the first side portion 98 contactsthe substrate 78 corresponds to the first tilted position (FIG. 17).When the bias voltage is applied to the second setting electrode 90, thetransducer 70 pivots until the second side portion 100 contacts thesubstrate 78 or the insulator layer 94 on the substrate 78. Theorientation of the transducer 70 when the second side portion 100contacts the substrate 78 corresponds to the second tilted position(FIG. 18). In alternative embodiments, other structures may beincorporated onto the substrate and/or the bottom of the lower electrodeto serve as stops for limiting the movement of the transducer toward thesubstrate and setting the first and second tilted positions.

In an unbiased state, the transducer 70 is oriented substantiallyparallel to the upper surface 96 of the substrate 78, as can be seen inFIGS. 15 and 16, which results in the transducer 70 having substantiallya 0° angle of incidence with respect to the blood vessel. When thetransducer is in the first tilted position, the transducer 70 isoriented in a first direction at an angle of incidence α that is greaterthan 0° and less than 90°. When the transducer 70 is in the secondtilted position, the transducer 70 is oriented in the opposite directionat the same angle of incidence α. In alternative embodiments, the angleof incidence of the transducer may be different in the first and secondtilted positions. This may be accomplished by incorporating asymmetricstops or limit structures onto the device for limiting movement of thetransducer to different degrees in the different directions of tilt.

The micro-mechanical adjustment system 80 can be used to compensate formisalignment of the transducer 70 with respect to the blood vessel 30 ina similar manner as described above with regard to the phased arraytransducer of FIGS. 5-10. In this embodiment, movement of the transducer70 to the angles θ₁ and θ₂ is accomplished mechanically via themicro-mechanical adjustment system 80 by application of the bias voltageto the appropriate setting electrode 90, 92. Beam steering with phaseshifting is then used to find the measurement angles ϕ₁, ϕ₂ where theblood vessel is located for the angles θ₁ and θ₂. The distances to theblood vessel at the first and the second measurement angles ϕ₁, ϕ₂ canthen be determined which enables the blood flow direction to beidentified. Because the central axis of the array is known, themisalignment angle β can be determined so that the misalignment can becompensated for in calculating the radial component of the bloodvelocity.

In the embodiment of FIGS. 14-18, because the angle of incidence isadjusted mechanically, beam steering is not required to redirect thebeam so the array of transducers needs fewer transducers along the Xaxis. Therefore, in one embodiment, the array of transducers has a widthalong the X axis corresponding to one transducer element. The number oftransducers along the Y axis may be any suitable number that providesthe desired angle resolution and aperture size for finding themeasurement angle where the blood vessel is located.

The micro-mechanical adjustment system 80 of the embodiment of FIGS.14-18 is configured to enable mechanical adjustments of only one angleof the transducer. In alternative embodiments, mechanical adjustmentsystems may be configured to enable mechanical adjustments of only themeasurement angle of the transducer while enabling adjustments of theincident angle by beam steering with phase shifting.

In another alternative embodiment, the micro-mechanical adjustmentsystem may be configured to enable mechanical adjustments of both theangle of incidence and the measurement angle of the transducer. Thetransducer array comprises an array of piezoelectric transducerelements, such as depicted in FIGS. 5-7. The array may comprise a 1×Narray, an N×1 array, or an M×N array.

In this embodiment, the adjustment system and the transducer may beconfigured similar to a two-axis micro-mirror to enable tilting of thetransducer about two perpendicular axes. This embodiment eliminates theneed for phase shifters all together as beam steering is not required toadjust the angles of the transducer.

Another embodiment of a system 108 for detecting blood velocity andmeasuring blood pressure is depicted in FIG. 19. In this embodiment, thepiezoelectric transducer arrangement of the system is configured toimplement both a multi-input multi-output (MIMO) ultrasonic transducerarray and a phased transducer array. The system includes at least oneultrasonic transducer array 110, a phased array control system 112 and aMIMO array control system 114.

The transducer array 110 may comprise any number of elements along the Xaxis and Y axis of the array. For example, the array may comprise a 1×Narray, an N×1 array, or an M×N array, as depicted in FIGS. 5-7,respectively. The elements in the array may also be shifted, staggeredor offset from each other in either direction.

The system 108 may comprise a monostatic system in which the transducerarray 110 is used for both transmitting and receiving ultrasonicsignals. Alternatively, the system may comprise a bistatic system asdepicted in FIG. 20. In a bistatic system, a first ultrasonic transducerarray 110 a serves as the transmitter for the system and a secondultrasonic transducer array 110 b serves as the receiver for the system.

Transducers used to transmit are operably coupled to receive electricalsignals from the phased array control system 112 a and the MIMO arraycontrol system 114 a. Transducers used to receive output electricalsignals to the phased array control system 112 b and the MIMO arraycontrol system 114 b. The phased array control system 112 b and the MIMOarray control system 114 b are configured to process the electricalsignals using various techniques and algorithms known in the art todetermine information about the blood vessel.

The piezoelectric transducer elements of the array can have the sameconfiguration as any of the transducer elements of the embodimentsdiscussed above. Using the transducer element of FIG. 11 as an example,each transducer element of the array includes a piezoelectric substrate50, an upper electrode 52 and a lower electrode 54. The upper and lowerelectrodes 52, 54 are formed of a conductive material, such aspoly-silicon. The piezoelectric substrate 50 is formed of a suitablepiezoelectric material, such as lead zirconate titanate or aluminiumnitride. In one embodiment, each transducer element has substantiallythe same size and shape with the shape of each element being rectangularor square.

To avoid grating lobes when the transducer array is operated as a phasedarray, the pitch distance between the centers of adjacent elements inthe array is advantageously smaller than half the wavelength of thesignal emitted by the array. As noted above, for a transducer array tobe operated around a frequency of 4 MHz, the wavelength is approximately0.80 mm. Therefore, the pitch should be approximately 400 μm.

The phased array control system 112 a is configured to supply thetransmitting transducers with the same electrical signal, or waveform,with phase shifting and amplitude setting to direct an ultrasonic beamin the desired direction. The use of multiple transducers to transmitand receive the same signal results in significant transducer gain andgood signal quality.

The MIMO array control system 114 a is configured to supply each of thetransmitting transducers with an arbitrary waveform. To this end, theMIMO array control system 114 a includes a waveform generator (notshown) for each of the transducers. The waveform generators areconfigured to generate different waveforms for each of the transducers.These waveforms can be either correlated or uncorrelated with each otherand can be separated in the temporal, spectral, and/or spatial domains.It is also important that the waveforms do not interfere with eachother. One way to accomplish this is with a time-division multiplexing(TDM)-switched MIMO.

Each receiving transducer receives reflected signals from each of thetransmitting transducers. Due to the different wave forms, the reflectedsignals can be associated with the transmitting transducer which emittedthem. A transmitting array of N transducers and a receiving array of Ktransducers results in a K×N virtual array from K+N elements. Thisenables MIMO arrays to have large virtual apertures and a higher angleof resolution than corresponding phased arrays.

The phased array and MIMO array control systems may each include aprocessor (not shown), such as a central processing unit, an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) device, or a micro-controller. The processor may be configured toexecute programmed instructions that are stored in the memory (notshown). The instructions include instructions for phase shifting and/orfor implementing one or more beam steering algorithms.

The blood velocity detection system 108 includes a switching devices 116a, 116 b that are configured to switch the inputs to the transmittingarrays 110 a and the outputs of the receiving arrays 110 b between thephased array control system 112 a, 112 b and the MIMO array controlsystem 114 a, 114 b, respectively, so that the transducer arrays can beoperated as both a phased transducer array and a MIMO transducer arrayas needed. Any suitable switching configuration and/or methodology maybe used for the switching devices 116 a, 116 b.

In operation, the inputs to the transducer arrays are first switched tothe MIMO array control system 114 so that the transducer array 110 isoperated as a MIMO transducer array. The MIMO array control system 114supplies the transmitting transducers 110 a with arbitrary distinctwaveforms which causes the transducers to emit ultrasonic signals whichare directed roughly in the direction of the blood vessel. Reflectedsignals are received by the receiving transducers 110 b. The MIMO arraycontrol system 114 evaluates the output of the receiving transducers tolocate the blood vessel.

The input to the transducer arrays 110 a, 110 b are then switched to thephased array control system 112 a, 112 b so that the transducer array isoperated as a phased transducer array to take advantage of the hightransducer gains and better signal quality of the phased transducerarray and because the incident and outgoing beam can be directed by beamsteering with phase shifting.

One object of the combined MIMO array and phased array blood velocitydetection system is avoiding the use of high resolution algorithms, suchas multiple signal classification (MUSIC) algorithms. To accomplishthis, the transducers may be actuated as a sparse transducer array. Thetransducer array may be operated as a sparse array by omitting some ofthe transducer elements from being actuated to produce ultrasonicsignals. In one embodiment, the transducers may be omitted fromactuation as part of the MIMO transducer array in a random pattern sothat different pitches, or spacings, are provided between elements inthe array. The sparse spacing allows even larger virtual aperture sizeswhich in turn results in higher angle resolutions. This gives theopportunity to achieve a better spatial/angle resolution and make abetter angle estimation so that the blood vessel is located with greateraccuracy.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, the same should be considered asillustrative and not restrictive in character. It is understood thatonly the preferred embodiments have been presented and that all changes,modifications and further applications that come within the spirit ofthe disclosure are desired to be protected.

What is claimed is:
 1. A system for detecting blood velocity within ablood vessel, the system comprising: a transducer array configured to beplaced on an area of skin of a person over the blood vessel, thetransducer array including a plurality of ultrasonic piezoelectrictransducers, each of the piezoelectric transducers including: a carriersubstrate having an upper surface; a first spacer and a second spacerextending upwardly from the upper surface; a transducer elementsupported above the upper surface of the carrier substrate by the firstspacer and the second spacer, and the transducer element is spaced apartfrom the upper surface of the substrate; an upper electrode positionedon an upper surface of the transducer element facing away from thecarrier substrate; a lower electrode positioned on a lower surface ofthe transducer element facing toward the carrier substrate; and settingelectrodes positioned on the upper surface of the substrate under thetransducer element, and the setting electrodes configured to receive abias voltage, wherein the bias voltage being configured to create apotential difference between the setting electrodes and the lowerelectrode and the transducer element is configured to pivot about apivot axis between a first tilted position and a second tilted positionby the potential difference, wherein the first spacer and the secondspacer are each positioned on the upper surface outside of a region overwhich the transducer element is located, the first spacer beingconnected to a first lateral portion of the transducer element by afirst support arm that extends from an upper portion of the firstspacer, the second spacer being connected to a second lateral portion ofthe transducer element by a second support arm that extends from anupper portion of the second spacer, and wherein the transducer elementdefines a first angle with respect to the blood vessel in the firsttilted position and a second angle with respect to the blood vessel inthe second tilted position.
 2. The system of claim 1, wherein thesetting electrodes include a first setting electrode and a secondsetting electrode, the first setting electrode being positioned under afirst side portion of the transducer element, the first side portionbeing located on a first side of the pivot axis, the second settingelectrode being positioned under a second side portion of the transducerelement, the second side portion being located on a second side of thepivot axis.
 3. The system of claim 2, wherein, in the first tiltedposition, the transducer element defines a first angle of incidence withrespect to the blood vessel, and, in the second tilted position, thetransducer element defines a second angle of incidence with respect tothe blood vessel.
 4. The system of claim 3, further comprising: a phasecontrol system configured to cause the transducer array to emit anultrasonic beam, the phase control system being configured to steer theultrasonic beam along a Y-axis of the transducer array to locate ameasurement angle for the transducer array where the blood vessel islocated.
 5. The system of claim 1, wherein the upper electrode and thelower electrode are formed of poly-silicon.
 6. The system of claim 2,wherein the carrier substrate includes an insulation layer on an uppersurface of the substrate, and wherein the setting electrodes are formedin the insulation layer.
 7. The system of claim 6, wherein the carriersubstrate is formed of silicon.
 8. The system of claim 6, wherein thelower electrode is positioned in contact with the insulation layer whenthe transducer element is in the first tilted position and the secondtilted position.
 9. A method of compensating for misalignment of atransducer array with respect to a blood vessel, the method comprising:placing the transducer array on an area of skin, the transducer arrayincluding a plurality of transducers, each of the transducersrespectively including: a carrier substrate having an upper surface; afirst spacer and a second spacer extending upwardly from the uppersurface; a transducer element supported above the upper surface of thecarrier substrate by the first spacer and the second spacer, and thetransducer element is spaced apart from the upper surface of thesubstrate; an upper electrode positioned on an upper surface of thetransducer element facing away from the carrier substrate; a lowerelectrode positioned on a lower surface of the transducer element facingtoward the carrier substrate; and setting electrodes positioned on theupper surface of the substrate under the transducer element; locating afirst measurement angle at which the blood vessel is located by steeringan ultrasonic beam emitted by the transducer array with a phase controlsystem with the respective transducer elements in a first tiltedposition; applying a bias voltage to the setting electrodes of therespective transducers to create a potential difference between thetransducer element of the respective transducers and the lower electrodeof the respective transducers, the potential difference causing therespective transducer elements to pivot from the first tilted positionto a second tilted position; locating a second measurement angle atwhich the blood vessel is located by steering the ultrasonic beamemitted by the transducer array with the phase control system; anddetermining a misalignment angle for the transducer array based on thefirst measurement angle and the second measurement angle.
 10. The methodof claim 9, wherein the first tilted position defines a first angle ofincidence for the transducer element, and wherein the second tiltedposition defines a second angle of incidence for the transducer element.11. The method of claim 9, wherein the setting electrodes include afirst setting electrode and a second setting electrode, the firstsetting electrode being positioned under a first side portion of thetransducer element, the first side portion being located on a first sideof a pivot axis, the second setting electrode being positioned under asecond side portion of the transducer element, and the second sideportion being located on a second side of the pivot axis.
 12. The methodof claim 9, wherein the upper electrode and the lower electrode areformed of polysilicon.
 13. The method of claim 12, wherein the carriersubstrate is formed of silicon.
 14. The method of claim 13, wherein thecarrier substrate includes an insulation layer on an upper surface ofthe substrate, and wherein the setting electrodes are formed in theinsulation layer.
 15. The method of claim 14, wherein the lowerelectrode is positioned in contact with the insulation layer when thetransducer element is in the first tilted position and the second tiltedposition.